1. Field of the Invention
The invention generally relates to query routing in federated information systems, and, more particularly, to query routing in federated information systems designed to optimize response time and load balance while considering remote source availability and remote source reliability.
2. Description of the Related Art
Federated query optimizers often deploy cost-based query optimization mechanisms. Specifically, these optimizers can determine multiple global query execution plans and, then, select the execution plan with the lowest execution cost. Thus, cost functions indirectly influence what remote sources are accessed to retrieve data and how federated queries are processed. However, in many federated information systems, the cost function is based on database statistics and query statements without consideration of remote system availability and remote system reliability. Such systems also do not consider the dynamics of the runtime and workload environments. Furthermore, the approach of selecting the global query execution plan with the lowest cost and applying this plan to all similar queries is not necessarily ideal. For example, such an approach does not allow workloads to be distributed among alternative servers to achieve better load balance. Therefore, there is a need for a method, a computer program and a system for query routing in federated information systems that are each designed to optimize response time and load balance while also considering remote source availability and remote source reliability.